This invention relates to phenolic foams and particularly to closed-cell foams of a phenol/formaldehyde resin with a high degree of cure.
The use of foam materials as insulation is an already well-established expedient. However many foam materials that are currently in use have certain inherent problems such as flammability or the production of noxious gases on partial combustion. For this reason there have been a number of attempts to develop a foam with an inbuilt resistance to burning and at the same time high insulation value.
One of the resins explored as having the desired characteristics for producing a flame-resistant foam is a phenolic resin by which is meant in the context of this application a resole produced by the base-catalyzed copolymerization of phenol with an excess of formaldehyde.
Unfortunately the problems of producing a phenolic foam are substantial in that, if good thermal conductivity is to be maintained, substantially all the cells must be and remain closed. This is not easy since the reaction of phenol with formaldehyde generates water as a by-product and this can easily blow open the cells and so diminish the value of the foam as a thermal barrier.